Relationship between CRISPR sequence type and antimicrobial resistance in avian pathogenic Escherichia coli.

Avian pathogenic Escherichia coli (APEC) is a primary cause of extraintestinal disease and respiratory infections in chickens; therefore, various antimicrobials applied via mass medication in farms to control APEC in Korea. In this study, we analyzed the relationship between CRISPR sequence type and antimicrobial resistance (AMR) in APEC isolates. Based on spacer distribution, a total of 103 CRISPR-positive APEC isolates were classified into 25 E. coli sequence types (ESTs), largely into two clusters that were correlated with phylogenetic groups: isolates appearing to have CRISPR 1 and/or 2 (93.2 %) and those having CRISPR 3 and 4 (6.8 %). Moreover, ESTs were divided into three AMR pattern-based groups: cephems-resistant group, non-cephems-resistant group, and antimicrobial sensitive group. There were significant differences among the groups (p < 0.05). Sixteen of the 25 ESTs had a significantly higher distribution of multidrug-resistant (MDR) isolates than the other ESTs (p < 0.05), and the ratio of MDR isolates was significantly higher than that of non-MDR isolates in the CRISPR 1 and 2 arrays (p < 0.05). A total of 9 protospacers were identified with protospacer, with protospacer 1 in CRISPR 1 being the most prevalent among the isolates (41.7 %). The protospacers of CRISPR 1 and 2 loci were associated with protection against external invaders such as bacteriophage or endogenous gene regulation. However, each protospacer of the CRISPR 3 and 4 loci originated from genes associated with AMR plasmids. These results indicate that CRISPR sequence type can improve AMR bacteria and enhance strategies for tackling the complexity of AMR in bacterial pathogens.